In modern communication systems, transmitting a signal commonly involves mixing the signal with another signal of a given frequency and phase in order to modulate the signal to be transmitted. Similarly, the demodulation of a received signal also usually involves mixing the signal with another signal of a given frequency and phase. Previously, transmitters and receivers were discrete components. With improvements in IC (integrated circuit) technology, today there are various transceivers that combine the transmit and receive functions into one device.
FIG. 1 is a block diagram illustrating a transceiver. Receiver 100 receives a signal that is filtered by filter 105, and mixed by mixer 107 with a signal generated by LO (local oscillator) 120. The LO includes a TCXO (temperature controlled crystal oscillator) 130 and a PLL (phase locked loop) 135. The resulting signal is filtered by filter 170 and mixed by mixer 165 with another signal generated by LO 160 for further demodulation. LO 160 includes a TCXO 150 and a PLL 155. The demodulated baseband signal is sent to other parts of the device for further processing. In some embodiments, LO 120 and LO 160 share the same TCXO.
In transmitter 102, an input signal is filtered by filter 108, and mixed by mixer 109 with a signal generated by LO 122. The LO includes a TCXO 132 and a PLL 137. The signal generated by the LO is used to modulate the baseband signal. The IF modulated signal is filtered and mixed by mixer 167 with a signal generated by LO 162. LO 162 includes TCXO 152 and PLL 157. The RF modulated signal is amplified by power amplifier (PA) 169 and then transmitted.
Generally, it is desirable to design transceivers with as few components as possible to improve power consumption and reduce size. It would be useful if a smaller, more efficient transceiver could be developed.